Saturday, 7 May 2016

Digging extension foundations

We hired a 1.5t minidigger and a skip-lifter for the weekend in order to dig out the foundations for the new extension.

We've planned to have a continuous floor level from the doorway you can see at the top right of the below photo, to future-proof the new bathroom and study for less-able people. 

We hit thick yellow clay mixed with rocks after 6 inches of gravel (the previous extension's foundations!) and it took some serious skill on the digger (not by me, I should add) to get the area clear and vaguely level.

Once we were down 18in from finished floor level, we set about planning the foundation trench, which will be a further 18in deep, 2ft wide, and be filled with reinforced concrete.

Getting the digger to work at any sort of decent angle to the trench in an area 4m x 7m was hard work, and the trench was slow-going.

In the end we decided that a slope-sided trench would have to do, and gives us the option to shutter and backfill the sides if needs be later.

By the end of day 3 it was as complete as we could do with a digger. The rest would have to be done by hand. And as you can see we're considerably lower than previous ground level.

In fact, that ground level thing through up a bit of a nasty surprise. We'd often wondered what the large concrete moulding on the end of the house is. I finally twigged its importance today! 

When the house was built, it was built in to a hill. Original ground level was at the height of the line 18 inches up the concrete moulding (where it goes smooth). 

At some point in the past, that 18in of clay has been removed to increase drainage and allow for a walkway around the side of the house.

BUT, the house has no foundations, and only a couple of courses of large stones which were originally in the ground! What you can see in the picture below is it... there is no more stone beneath those walls - only clay and small rocks.

Suffice to say that, once I discovered that, all work on the digging stopped.

You can see in the photo below, towards the barrow, a dark line on the wall. That's the sub-foundation clay on show. It was quickly covered back up to keep it from drying out, and what you can't really see in these photos is that the digging-out from that point comes outwards at 45-degrees, so structurally we're still dissipating the weight of the house OK.

However, this does put any plan of having a floor which is level with the bottom of the door (far right of the pic above) out of the question. We're going back to the drawing board with the extension and re-planning the internals with a step up at some point.

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